This invention relates to fluid inlet grilles that are constructed to span a fluid flow inlet and allow fluid to flow through the fluid flow inlet while preventing large objects from passing through the fluid flow inlet. Such fluid inlet grilles have a plurality of grille bars, each of which extends across a portion of the fluid flow inlet that the fluid inlet grille spans. A plurality of fluid flow spaces, through which fluid may flow, are defined between the grille bars of such fluid inlet grilles within the fluid flow inlet spanned by the fluid inlet grille. Objects larger than the fluid flow spaces defined between the grille bars of the fluid inlet grille are prevented from traveling through the fluid flow inlet. The use of such fluid inlet grilles is well known in many different applications. One application where such fluid inlet grilles are used, for example, is in vehicles. Many vehicles have a fluid flow inlet that is defined between body panels of the vehicle and that is disposed in front of one or more heat exchangers such as radiators, air conditioner condensers, charge air coolers, and/or transmission coolers. A fluid inlet grille mounted to a vehicle in such a manner allows the flow of fluid, which is usually air, through the fluid flow spaces between the grille bars and then through the heat exchangers disposed behind the fluid inlet grille. The grille bars of a fluid inlet grille mounted to a vehicle in such a manner also prevent large objects from traveling through the fluid flow inlet and damaging or restricting fluid flow through the heat exchangers disposed behind the fluid flow inlet.
In many applications of such a fluid inlet grille the fluid flow is most always in the same direction through the fluid flow inlet that the fluid inlet grille spans. The mounting of a fluid inlet grille to a vehicle to protect one or more heat exchangers mounted behind the fluid inlet grille, as described above, is one example of an application of a fluid inlet grille where the fluid flow is almost always in the same direction through the fluid inlet which the fluid inlet grille spans. In this application the fluid flow through the fluid flow inlet is almost always in a direction from in front of the fluid inlet grille, through the fluid flow inlet that the fluid inlet grille spans, and then toward and eventually through the one or more heat exchangers mounted behind the fluid inlet grille. For purposes of this disclosure the direction that fluid almost always flows toward and through a fluid flow inlet that a fluid inlet grille spans will be referred to as the prevailing fluid inflow direction. A fluid inlet grille that is used in such an application, in which there exists a prevailing fluid inflow direction, and its grille bars have opposite sides that may be considered an upstream side and a downstream side respectively. The upstream side of such a fluid inlet grille and its grille bars being the side that fluid first passes as it flows in the prevailing fluid inflow direction toward and through the fluid flow inlet which the fluid inlet grille spans. The downstream side of the fluid inlet grille and its grille bars being the side that fluid last passes as it flows in the prevailing fluid inflow direction through and away from the fluid flow inlet.
In many applications in which a fluid inlet grille is used the aerodynamic properties of the fluid inlet grille are important. It is generally desirable that the fluid inlet grille provide as little resistance to flow of the fluid through the fluid flow inlet as possible. It is also preferred that the fluid inlet grille is constructed in such a manner that the velocity distribution of the fluid flow evens out in as short a distance as possible from the downstream side of the fluid inlet grille. A vehicle that has a fluid inlet grille mounted in front of one or more heat exchangers, as described above, is an example of an application in which a fluid inlet grille is used and in which it is desirable that the fluid inlet grille have such aerodynamic properties. In such an application, all other factors being equal, reducing the resistance of the fluid inlet grille to the flow of fluid past it will result in increased velocity of the fluid flow after it has passed the fluid inlet grille and also as it passes through the heat exchangers mounted on the downstream side of the fluid inlet grille. Increased velocity of the fluid flow through the heat exchangers increases the rate of heat transfer and, thus, improves the performance of the heat exchangers. The uniformity of the velocity distribution of the fluid flow as it passes through the heat exchangers in such an application also affects the performance of the heat exchangers. The more uniform the velocity of the fluid flow through the heat exchangers is in directions perpendicular to the direction in which it is flowing, the better the performance of the heat exchangers will be. When fluid flows through a fluid flow inlet past a fluid inlet grille, there is a stagnation area adjacent the downstream side of each of the grille bars. The velocity of the fluid flow in the stagnation area downstream of each of the grille bars is substantially less than the velocity of the fluid flow to either side of the stagnation area in directions perpendicular to the flow of the fluid through the fluid inlet opening. The stagnation area behind each of the grille bars does, however, have a finite length and at some distance in the downstream direction from each grille bar the velocity of the fluid flow is equal to the velocity of adjacent portions of the fluid flow. If a heat exchanger is mounted upon the downstream side of a fluid inlet grille at a distance close enough to the fluid inlet grille that the stagnation area of one or more of the grille bars extends into the heat exchanger, the performance of the heat exchanger will be compromised. In such a situation, the fluid flow through those portions of the heat exchanger into which any stagnation areas of the grille bars extend will have a significantly lower velocity than the fluid flow through adjacent portions of the heat exchanger. In such a situation, less heat will be transferred between those portions of the heat exchanger that are disposed within a stagnation area downstream of a grille bar and the fluid flowing through them than will be transferred between adjacent portions of the heat exchanger and the fluid flowing through them. Thus, the overall performance of the heat exchanger is compromised when it is placed close enough to the fluid inlet grille that one or more portions of the heat exchanger are disposed within stagnation area(s) of the grille bars. As a result, many vehicles that have one or more heat exchangers mounted behind a fluid flow inlet, across which a fluid inlet grille spans, have the heat exchangers mounted sufficiently far enough away from the fluid inlet grille to be beyond the stagnation area of each of the grille bars of the fluid inlet grille. In many circumstances, however, space for mounting of components is at a premium on a vehicle and the need to place a heat exchanger at such a distance from a fluid inlet grille on its downstream side can increase the challenges of constructing a vehicle in a compact manner while providing all desirable features.